A liquid ejection head for ejecting liquid, in the form of a minute liquid droplet, has been widely employed as an ink jet head in the field of ink jet recording. Not only is an ink jet head required to simply eject liquid droplets, but also it is required to be stable in the direction in which liquid droplets are ejected. Thus, various proposals have been made to meet these requirements.
For example, Japanese Laid-open Patent Application 5-77422 discloses an ink jet head in which, in order to stabilize ink flight, ejection outlets for ejecting ink are placed in recesses, one for one, being in the center of the bottom of the recess to prevent the body of ink from a given ejection outlet from coming into contact with the body of ink from the ejection outlet adjacent thereto. Japanese Laid-open Patent Applications 5-193141 and 11-334069 also disclose an ink jet head in which ejection outlets are placed in recesses, one for one, being in the center of the bottom of the recess. In the case of this ink jet bead, the internal surface of the recess is treated to give it a strong affinity for ink, and the outward surface or the member having the ejection outlet member is treated to cause it to repel ink. This combination of the structural arrangement and surface treatments is intended to form a meniscus in the recess of the ejection outlet so that ink is rejected with the presence of the meniscus in the recess of the ejection outlet. This, according to the aforementioned applications, improves recording quality by stabilizing liquid ejection.
In recent years, the demand has further increased for improving an ink jet head in terms of image quality, in particular, in terms of graininess. Thus, in order to make as inconspicuous as possible the graininess resulting from the manner in which the ink droplets adhere to recording medium, a substantial amount of effort has been made to reduce the size of the droplet in which liquid is ejected. However, the above described ink jet head in accordance with the prior arts are not necessarily structured to substantially reduce liquid droplet size.
The primary object of the present invention is to provide a liquid ejection head which ejects extremely small liquid droplets, more specifically, liquid droplets, the sizes of which are on the order of no more than a pico-liter. Once a liquid ejection head capable of ejecting liquid droplets, the sizes of which are on the order of no more than a pico-liter, is realized, not only will the application or such a liquid ejection head quickly spread in the field of ink jet recording, but also it will spread into fields other than the field of ink jet recording.
According to an aspect of the present invention, there is provided a liquid ejection head comprising a liquid path; an ejection outlet forming member which constitutes a part of a wall of the liquid and which forms an ejection outlet for ejecting a droplet of liquid; a heat generating element, provided at a position opposing to said ejection outlet of the wall of said liquid flow path, for generating a bubble in the liquid by application of heat to the liquid; a restrictor portion, provided at a recessed portion of said ejection outlet, wherein said recessed portion is recessed from a plane in which said ejection outlet is formed, wherein the liquid forms a meniscus and is retained in said ejection outlet such that said restrictor portion is within the liquid, wherein an area So of an opening of said restrictor portion and a surface Sh of said heat generating element satisfy So≦Sh.
According to another aspect of the present invention, there is provided a liquid ejection head comprising a liquid path; an ejection outlet forming member which constitutes a part of a wall of the liquid and which forms an ejection outlet for ejecting a droplet of liquid; an energy generating element, provided at a position opposing to said ejection outlet of the wall of said liquid flow path, for generating ejection energy to be applied to the liquid; a restrictor portion, provided at a recessed portion of said ejection outlet, wherein said recessed portion is recessed from a plane in which said ejection outlet is formed, wherein the liquid forms a meniscus and is retained in said ejection outlet such that said restrictor portion is within the liquid, wherein a thickness c or said restrictor portion and a height e of said liquid path measured in a direction in which said ejection outlet and said energy generating element are faced to each other, satisfy c≦e.
According to a further aspect of the present invention, there is provided a liquid ejection head comprising a liquid path; an ejection outlet forming member which constitutes a part of a wall of the liquid and which forms an ejection outlet for ejecting a droplet of liquid; an energy generating element, provided at a position opposing to said ejection outlet of the wall of said liquid flow path, for generating ejection energy to be applied to the liquid; a restrictor portion, provided at a recessed portion of said ejection outlet, wherein said recessed portion is recessed from a plane in which said ejection outlet is formed, wherein the liquid forms a meniscus and is retained in said ejection outlet such that said restrictor portion is within the liquid, wherein a thickness c of said restrictor portion and a thickness d of said ejection outlet forming member measured between a plane in which said ejection outlet is formed and said restrictor portion, satisfy c≦d.
The position of the restrictor portion in the ejection outlet, in terms of the thickness direction of the member having the energy generating members is desired to be between the top and bottom surfaces of the member. Also, the hole of the restrictor portion is tapered so that the top opening of the hole is greater than that of the bottom opening of the hole, or vice versa. Further, the restrictor portion is desired to have a plurality of holes, as liquid passages, smaller than the other portions of the ejection outlet.
As for examples of liquid ejectable from a liquid ejection head, there are recording liquids used for ink jet recording, liquid medicines inhaled into lungs, etc.